1. Field of the Invention
The present application relates to a passive component, and particularly to an over-current protection device.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Because the resistance of conductive composite materials having a positive temperature coefficient (PTC) characteristic is very sensitive to temperature variation, it can be used as the material for current sensing devices, and has been widely applied to over-current protection devices or circuit devices. The resistance of the PTC conductive composite material remains extremely low at normal temperature, so that the circuit or cell can operate normally. However, when an over-current or an over-temperature event occurs in the circuit or cell, the resistance instantaneously increases to a high resistance state (e.g. at least 102Ω), so as to suppress over-current and protect the cell or the circuit device.
U.S. Pat. No. 6,713,210 disclosed a circuit board with over-current protection function. As shown in FIG. 1, an IC device 2 is placed on a protective circuit module (PCM) 1, and a PTC device 3 is surface-mounted on the PCM 1. The PTC device 3 is a stack structure in which a PTC material layer 6 is laminated between nickel foils (or nickel-plated copper foils) 7 and 7′. The nickel foils 7 and 7′ serve as electrodes for the PTC material layer 6. A nickel plate 4 serving as an external electrode is secured on the upper surface of the nickel foil 7, and a copper electrode 5 is soldered to the lower surface of the nickel foil 7′ that is adjacent to the surface of the PCM 1. The nickel plate 4 and the copper plate 5 are symmetrical with reference to the PTC device 3.
In consideration of high voltage and high current in spot-welding, the PTC device 3 cannot be subjected to spot-welding directly, and needs to be first combined with a nickel plate 4 of a thickness preferably greater than 0.3 mm, so as to avoid damage to the nickel foils 7 and 7′ of the PTC device 3 while spot-welding. However, the nickel plate 4 is usually attached to the PTC device 3 manually, which is detrimental to mass production and cost reduction.